1. Field of the Invention
The present invention relates to a semi-transmissive in-plane switching mode liquid crystal display panel and a method for fabricating the same, and more particularly, to a semi-transmissive in-plane switching mode liquid crystal display panel, in which each pixel region can exhibit the same luminance in transmissive and reflective portions thereof while having a single cell gap structure, and a method for fabricating the same.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices display an image by adjusting the light transmittance of liquid crystals. Such LCD devices are classified into a twisted nematic (TN) mode and an in-plane switching (IPS) mode.
In a TN mode LCD device, a common electrode formed on an upper substrate and a pixel electrode formed on a lower substrate are arranged to face each other. TN mode liquid crystals are driven by a vertical electric field generated between the common electrode and the pixel electrode.
Such a TN mode LCD device has an advantage of a high aspect ratio, but has a drawback of a narrow viewing angle of about 90°.
In order to solve the above-mentioned drawback of the TN mode LCD device, an IPS mode LCD device was proposed. In the IPS mode LCD device, liquid crystals are driven by a horizontal electric field generated between a pixel electrode and a common electrode formed on a lower substrate. In this case, large viewing angle characteristics of about 160° are obtained.
Hereinafter, the configuration and operation of an IPS mode LCD device will be described with reference to FIGS. 1 to 3.
As shown in FIG. 1, the IPS mode LCD device 70, in which liquid crystals are driven by a horizontal electric field formed between a pixel electrode and a common electrode, includes a thin film transistor (TFT) substrate 30 and a color filter substrate 50 assembled such that a liquid crystal layer is interposed between the TFT substrate 30 and the color filter substrate 50.
As shown in FIGS. 1 and 2, the TFT substrate 30 includes a lower substrate 31, a plurality of gate lines 32 formed on the lower substrate 31, common electrodes 35 connected to common lines 34 formed on the same layer as the gate lines 32, and data lines 37 formed to intersect the gate lines 32 such that a gate insulating film 36 is interposed between the data lines 37 and the gate lines 32. The gate lines 32 and data lines 37 define pixel regions. The TFT substrate 30 also includes TFTs formed at respective intersections of the gate lines 32 and data lines 37, a passivation film 42 covering the TFTs, pixel electrodes 43 formed on the passivation film 42, and a lower orientation film 44 covering the pixel electrodes 43. In each pixel region, one pixel electrode 43 and one common electrode 35 are arranged such that electrode portions thereof are alternately arranged.
Each TFT includes a gate electrode 33 connected to the associated gate line 32, a source electrode 38 connected to the associated data line 37, a drain electrode 39 formed to face the source electrode 38 at opposite sides of a channel, and a semiconductor pattern. The semiconductor pattern includes an active layer 40, which forms the channel, and an ohmic contact layer 41.
As shown in FIGS. 1 and 3, the color filter substrate 50 includes an upper substrate 51, a black matrix 52 formed on the upper substrate 51, to partition the pixel regions and to avoid the occurrence of a light leakage phenomenon, and color filters 53 respectively formed in the pixel regions partitioned by the black matrix 52. The color filter substrate 50 also includes an overcoating layer 54 removing steps formed by the color filters 53, to planarize an upper surface of the upper substrate 51, spacers 55 formed on the overcoating layer 54, to maintain a desired cell gap, and an upper orientation film 56.
Recently, a semi-transmissive IPS mode LCD device has been proposed. The semi-transmissive IPS mode LCD device is fabricated by additionally forming reflective electrodes in an IPS mode LCD device having the above-mentioned configuration. The reflective electrodes function to reflect light externally incident to the LCD device. Thus, each pixel region of the semi-transmissive IPS mode LCD device includes a transmissive portion where an image is displayed by incident light from a backlight unit, and a reflective portion where an image is displayed by light reflected by one reflective electrode.
Hereinafter, the configuration and operation of a conventional semi-transmissive IPS mode LCD device will be described with reference to FIG. 4.
In the semi-transmissive IPS mode LCD device, liquid crystals are driven by a horizontal electric field in each pixel region divided into a transmissive portion and a reflective portion. As shown in FIG. 4, the semi-transmissive IPS mode LCD device includes a TFT substrate 11 formed with a plurality of lines and a plurality of TFTs, a color filter substrate 21 arranged to face the TFT substrate 11, and a liquid crystal layer 15 filled in a cell gap defined between the two substrates 11 and 21.
The TFT substrate 11 includes gate lines and data lines formed such that they intersect each other, to define pixel regions, and TFTs formed at respective intersections of the gate lines and data lines. The TFT substrate 11 also includes an organic insulating film 18 formed in a reflective portion of each pixel region, a reflective electrode 60 formed on the organic insulating film 18, to reflect externally-incident light, a pixel electrode 17 formed at the same layer as the reflective electrode 60 in a transmissive portion of each pixel region, a passivation film 16 covering the reflective electrode 60 and pixel electrode 17, and a common electrode 24 formed on the passivation film 16, to generate a horizontal electric field in cooperation with the pixel electrode 17.
The above-mentioned semi-transmissive IPS mode LCD device has a dual cell gap structure in which the cell gap defined in the transmissive portion corresponds to about 2 times the cell gap defined in the reflective portion, due to the organic insulating film 60 formed in the reflective portion. By virtue of this dual cell gap structure, the phase difference between the reflective portion and the transmissive portion is compensated for. Thus, the same luminance characteristics are obtained in both the reflective and transmissive portions of each pixel region.
In order to form the dual cell gap structure, and thus to obtain the same luminance characteristics in both the reflective and transmissive portions of each pixel region, however, it is necessary to use an additional process for the formation of the organic insulating film 18 in the reflective portion. For this reason, the overall process is complex. Furthermore, a degradation in process efficiency occurs.